MacBook Green Screen issue

Hi all, I recently switched on my late 2011 MacBook Pro transferred a few files from the net, synced my iTunes with my iPod touch and as I was about to shut it down, the screen went green almost as if it was dropped on the floor or something, I clicked on the apple logo and it went back to normal so I continued with the shutdown. A few hours later I turned it on and was greeted by the green screen and this time no matter where I clicked, it seemed to stay that way. I am very sure it was not dropped because I keep it on the floor in it's bag away from anywhere where anyone can see, touch or step on it. So now I'm wondering what could cause this if it wasn't dropped before I have to pay an Arm and a Leg to get it repaired, I would really appreciate your insight as to what could have happened or how I can try solve it, please do find attached an image of what it looks like, I tried searching for a similar problem to no avail and I am new to this forum so I may have over looked something or missed on a specific detail, please do try bare with me.

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